event: ensure that modifications to items expected to be readonly have no effect

this isn't a very glorious fix, but it's the best I have for now.

src/event/player/PlayerInteractEvent.php

@@ -69,7 +69,7 @@ class PlayerInteractEvent extends PlayerEvent implements Cancellable{
 	}
 
 	public function getItem() : Item{
-		return $this->item;
+		return clone $this->item;
 	}
 
 	public function getBlock() : Block{

src/event/player/PlayerItemHeldEvent.php

@@ -60,6 +60,6 @@ class PlayerItemHeldEvent extends PlayerEvent implements Cancellable{
 	 * Returns the item in the slot that the player is trying to equip.
 	 */
 	public function getItem() : Item{
-		return $this->item;
+		return clone $this->item;
 	}
 }

src/event/player/PlayerItemUseEvent.php

@@ -47,7 +47,7 @@ class PlayerItemUseEvent extends PlayerEvent implements Cancellable{
 	 * Returns the item used.
 	 */
 	public function getItem() : Item{
-		return $this->item;
+		return clone $this->item;
 	}
 
 	/**